This invention relates to an internal combustion engine. More particularly, the invention relates to a piston for a reciprocating internal combustion engine. The invention also relates to a control system for a valve incorporated in a piston for an internal combustion engine
The invention has been devised particularly, although not exclusively, for an internal combustion engine of the type disclosed in U.S. Pat. No. 5,261,358, the contents of which are incorporated herein by way of reference.
With the abovementioned internal combustion engine, as also is the case with most reciprocating piston internal combustion engines, it is particularly desirable for fuel droplets to mix intimately with air in the combustion chamber. One way in which this can be achieved is by subjecting the air in the combustion chamber to a swirling motion.
With the abovementioned internal combustion engine, it is also desirable for scavenging air introduced into the combustion chamber to undergo turbulent flow in order to perform an effective scavenging process.
Furthermore, in the abovementioned engine, the scavenging air is introduced into the combustion chamber through a port in the piston which is opened and closed by a valve. There is a need for a simple yet effective system for controlling operation of the valve.
It is against this background that the present invention has been developed.
According to one aspect of the present invention there is provided a piston for an internal combustion engine, the piston comprising a piston head, a recess formed in the piston head, and a formation associated with the recess for generating a turbulent motion in a fluid introduced into the recess.
Preferably, the formation is configured to generate a swirling turbulent motion to the fluid introduced into the recess.
The formation may comprise at least one spiral groove formed in the piston. Preferably, there are a plurality of the spiral grooves disposed about the recess. Conveniently, each of the spiral grooves extends outwardly from the recess and tapers inwardly in the direction in which it spirals outwardly.
With this arrangement, combustion air contained in the combustion chamber is acted upon by the formation associated with the recess as the piston performs a compression stroke, thereby causing the combustion air to undergo a turbulent motion which promotes mixing between the air and fuel droplets delivered into the combustion chamber.
In the case of an engine in which scavenging air is introduced into the combustion chamber through a port in the head of the piston (as is the case with the abovementioned engine disclosed in U.S. Pat. No. 5,261,358), the formation may be arranged to impart a swirling motion to the scavenging air entering the combustion chamber and so assist the scavenging process.
With this arrangement, the port through which the scavenging air is introduced into the combustion chamber may open into the recess such that the incoming scavenging air is subjected to the influence of the formation.
The port may be opened and closed by a valve which is operable under the influence of a control system.
The control system may include a hydraulic lifter operable by a hydraulic fluid such as oil (which may, for example, be oil used for lubricating the engine). The control system may further include a fluid flow path along which hydraulic fluid is delivered to the hydraulic lifter, the fluid flow path including a first section and a second section. The second section is located in the piston and opens onto a side wall thereof. The first section is located in part of the engine with respect to which the piston can reciprocate, and opens onto a side wall of the cylinder in which the piston is housed. With this arrangement, the second section registers with the first section for a limited period during reciprocation of the piston. When the piston is performing an expansion stroke and there is registration between the two sections of the fluid flow path, hydraulic fluid flows from the first section to the second section thereby to cause operation of the valve lifter.
A bleed path may be associated with the second section to allow hydraulic fluid to bleed therefrom.
The control system may further include a spring means for biasing the valve to a closed condition in relation to the port. Once the two sections of the fluid flow path have moved out of registration, the influence of the spring means causes the valve to return to the closed condition, with hydraulic pressure on the valve lifter being relieved by fluid bleeding from the second section.
According to a second aspect of the invention, there is provided an internal combustion engine having a piston according to the first aspect of the invention.
According to a third aspect of the invention there is provided a piston for an internal combustion engine, the piston comprising: a port formed in the head thereof through which a fluid can be delivered into a combustion chamber; a valve for opening and closing the port; and a formation in the piston head for imparting a swirling motion to fluid delivered into the combustion chamber through the port upon opening thereof.
Preferably, the port is accommodated in a recess formed in the piston, the formation comprising a plurality of spiral grooves formed in the piston about the recess.
The valve for opening and closing the port of the piston according to the third aspect of the invention may be operable under the influence of a control system as defined hereinbefore.
According to a fourth aspect of the invention, there is provided an internal combustion engine having a piston according to the third aspect of the invention.
According to a fifth aspect of the invention there is provided a piston for an internal combustion engine, the piston comprising: a port formed in the head thereof through which a fluid can be delivered into a combustion chamber; a valve for opening and closing the port; and a control system for operating the valve, the control system including a hydraulic lifter operable by a hydraulic fluid such as oil (which may, for example, be oil used for lubricating the engine), the control system further including a fluid flow path along which hydraulic fluid is delivered to the hydraulic lifter, the fluid flow path having a first section and a second section, the second section being located in the piston and opening onto a side wall thereof, and the first section being located in part of the engine with respect to which the piston can reciprocate and opening onto a side wall of the cylinder in which the piston is housed, whereby the second section can register with the first section for a limited period during reciprocation of the piston such that when the piston is performing a prescribed stroke and there is registration between the two sections of the fluid flow path, hydraulic fluid can flow from the first section to the second section thereby to cause operation of the valve lifter.
According to sixth aspect of the invention, there is provided an internal combustion engine having a piston according to the fifth aspect of the invention.